1. Field of the Invention
This invention relates to compounds for the inhibition of histone deacetylase.
2. Description of Related Art
In eukaryotic cells, nuclear DNA associates with histones to form a compact complex called chromatin. The histones constitute a family of basic proteins which are generally highly conserved across eukaryotic species. The core histones, termed H2A, H2B, H3, and H4, associate to form a protein core. DNA winds around this protein core, with the basic amino acids of the histones interacting with the negatively charged phosphate groups of the DNA. Approximately 146 base pairs of DNA wrap around a histone core to make up a nucleosome particle, the repeating structural motif of chromatin.
Csordas, Biochem. J., 286: 23-38 (1990) teaches that histones are subject to posttranslational acetylation of the N-terminal lysine residues, a reaction that is catalyzed by histone acetyl transferase (HAT1). Acetylation neutralizes the positive charge of the lysine side chain, and is thought to impact chromatin structure. Indeed, Taunton et al., Science, 272: 408-411 (1996), teaches that access of transcription factors to chromatin templates is enhanced by histone hyperacetylation. Taunton et al. further teaches that an enrichment in underacetylated histone H4 has been found in transcriptionally silent regions of the genome.
Histone acetylation is a reversible modification, with deacetylation being catalyzed by a family of enzymes termed histone deacetylases (HDACs). The molecular cloning of gene sequences encoding proteins with HDAC activity has established the existence of a set of discrete HDAC enzyme isoforms. Grozinger et al., Proc. Natl. Acad. Sci. USA, 96:4868-4873 (1999), teaches that HDACs may be divided into two classes, the first represented by yeast Rpd3-like proteins, and the second represented by yeast Hd1-like proteins. Grozinger et al. also teaches that the human HDAC-1, HDAC-2, and HDAC-3 proteins are members of the first class of HDACs, and discloses new proteins, named HDAC-4, HDAC-5, and HDAC-6, which are members of the second class of HDACs. Kao et al., Gene & Development 14:55-66 (2000), discloses an additional member of this second class, called HDAC-7. More recently, Hu, E. et al. J. Bio. Chem. 275:15254-13264 (2000) disclosed another member of the first class of histone deacetylases, HDAC-8. Zhou et al., Proc. Natl. Acad. Sci. U.S.A., 98: 10572-10577 (2001) teaches the cloning and characterization of a new histone deacetylase, HDAC-9. Kao et al., J. Biol. Chem., 277:187-93 (2002) teaches the isolation and characterization of mammalian HDAC10, a novel histone deacetylase. Gao et al, J. Biol. Chem. (In press) teaches the cloning and functional characterization of HDAC11, a novel member of the human histone deacetylase family. Shore, Proc. Natl. Acad. Sci. U.S.A. 97: 14030-2 (2000) discloses another class of deacetylase activity, the Sir2 protein family. It has been unclear what roles these individual HDAC enzymes play.
Studies utilizing known HDAC inhibitors have established a link between acetylation and gene expression. Numerous studies have examined the relationship between HDAC and gene expression. Taunton et al., Science 272:408-411 (1996), discloses a human HDAC that is related to a yeast transcriptional regulator. Cress et al., J. Cell. Phys. 184:1-16 (2000), discloses that, in the context of human cancer, the role of HDAC is as a corepressor of transcription. Ng et al., TIBS 25: March (2000), discloses HDAC as a pervasive feature of transcriptional repressor systems. Magnaghi-Jaulin et al., Prog. Cell Cycle Res. 4:41-47 (2000), discloses HDAC as a transcriptional co-regulator important for cell cycle progression.
Richon et al., Proc. Natl. Acad. Sci. USA, 95: 3003-3007 (1998), discloses that HDAC activity is inhibited by trichostatin A (TSA), a natural product isolated from Streptomyces hygroscopicus, which has been shown to inhibit histone deacetylase activity and arrest cell cycle progression in cells in the G1 and G2 phases (Yoshida et al., J. Biol. Chem. 265: 17174-17179, 1990; Yoshida et al., Exp. Cell Res. 177: 122-131, 1988), and by a synthetic compound, suberoylanilide hydroxamic acid (SAHA). Yoshida and Beppu, Exper. Cell Res., 177: 122-131 (1988), teaches that TSA causes arrest of rat fibroblasts at the G1 and G2 phases of the cell cycle, implicating HDAC in cell cycle regulation. Indeed, Finnin et al., Nature, 401: 188-193 (1999), teaches that TSA and SAHA inhibit cell growth, induce terminal differentiation, and prevent the formation of tumors in mice. Suzuki et al., U.S. Pat. No. 6,174,905, EP 0847992 and JP 258863/96, disclose benzamide derivatives that induce cell differentiation and inhibit HDAC. Delorme et al., WO 01/38322 and WO 2001/070675, disclose additional compounds that serve as HDAC inhibitors. Other inhibitors of histone deacetylase activity, including trapoxin, depudecin, FR901228 (Fujisawa Pharmaceuticals), and butyrate, have been found to similarly inhibit cell cycle progression in cells (Taunton et al., Science 272: 408-411, 1996; Kijima et al., J. Biol. Chem. 268(30):22429-22435, 1993; Kwon et al., Proc. Natl. Acad. Sci. USA 95(7):3356-61, 1998).
Research in the past decade has uncovered a new classification of inherited neurodegenerative diseases, the polyglutamine (polyQ) expansion diseases. In each, the underlying mutation is an expansion of a CAG trinucleotide repeat that encodes polyQ in the respective disease protein. All are progressive, ultimately fatal disorders that typically begin in adulthood and progress over 10 to 30 years. The clinical features and pattern of neuronal degeneration differ among the diseases, yet increasing evidence suggests that polyQ diseases share important pathogenic features. In particular, abnormal protein conformations promoted by polyQ expansion seem to be central to pathogenesis. This class of PolyQ expansion neurodegenerative disease are Huntington's Disease (HD), Dentatorubralpallidoluysian atrophy (DRPLA), spinal and bulbar muscular atrophy (SBMA), and five spinocerebellar ataxias (SCA1, SCA2, SCA3/MJD (Machado-Joseph Disease), SCA6 and SCA7).
It is known that certain HDAC inhibitors, for example SAHA, CBHA and pryoxiamide can cross the blood brain barrier at sufficient amounts to significantly inhibit HDAC activity causing the accumulation of acetylated histones in the brain (WO 03/032921). This discovery therefore provides for the use of HDAC inhibitors for inhibiting HDAC in the brain, for the treatment of polyglutamine (polyQ) expansion diseases.
The art provides data that HDAC inhibitors are promising novel therapeutics for polyglutamine expansion diseases. Other data support a therapeutic benefit of HDAC inhibitors for Huntington's disease. Sadri-Vakili and Cha (Nature Clinical Practice Neurology, 2006, 2(6):330-338), and references cited therein, for example, review the current state of knowledge regarding the status of histones in Huntington's Disease and teach that recent studies have shown a therapeutic role for hisone deacetylase inhibitors in a number of Huntington's Disease models. In vivo, HDAC inhibitors arrest ongoing progressive neuronal degeneration induced by polygluatmine repeat expansion, and they reduce lethality in two Drosophila models of polyglutamine disease (Steffan et al., 2001, Nature 413: 739-743). Similar findings were observed with sodium butyrate and TSA (Zhao et al., 2005, J. Expt. Biol., 208:697-705). Gardian et al. (2005, J. Biol. Chem., 280:556-563) showed that phenylbutyrate is capable of improving survival and attenuating brain atrophy in the N171-82Q transgenic mouse model of Huntington's Disease. In the R6/2 model of Huntington's Disease, sodium butyrate extended survival, improved motor deficits and delayed neuropathological sequelae (Ferrante et al., 2003, J. Neurosci., 23:9418-9427). In that same model, suberoylanilide hydroxamic acid (SAHA) was also active in improving the motor impairment (Hockly, 2003, Proc. Natl. Acad. Sci. USA, 100:2041-0246). Ying et al. (2005, J. Biol. Chem., 281:12580-12586) showed that sodium butyrate improved life span and motor deficits in a mouse model for DRPLA. Bates et al. (2006, The Journal of Neuroscience, 26(10):2830-2838) reported that in Caenorhabditis elegans expressing a human huntingtin fragment with an expanded polyglutamine tract (Htn-Q150), knockdown of C. elegans hda-3 suppressed Htn-Q150 toxicity. Neuronal expression of hda-3 restored Htn-Q150 toxicity and suggested that C. elegans HDAC3 acts within neurons to promote degeneration in response to Htn-Q 150.
These findings suggest that inhibition of HDAC activity represents a novel approach for intervening in cell cycle regulation and that HDAC inhibitors have great therapeutic potential in the treatment of polyglutamine (polyQ) expansion diseases, such as Huntington's Disease. It would be highly desirable to have novel inhibitors of histone deacetylase.